Abstract: The sidelobe reduction by using the unequal spacing of elements is studied. A new method for the calculation of optimum unequal spaced array in such sence that the sidelobe level is the lowest and the 3dB beamwidth is the narrowest for specific sidelobe level is presented. Some other directivity functions required in practice can be obtained by this method. Numerical calculations of some unequal spaced arrays are made. Some properties of the unequally spaced array are discussed in detail.